In recent years, a technology called OpenFlow has been proposed (refer to Patent Literatures 1 and 2, and Non-Patent Literatures 1 to 3). OpenFlow treats communication as an end-to-end flow, and performs path control, failure recovery, load balancing, and optimization for each flow. An OpenFlow switch that functions as a relay device comprises a secure channel for communicating with an OpenFlow controller, a control device, and operates according to a flow table suitably added or rewritten by the OpenFlow controller. In the flow table, a set of matching rules (Header Fields) matching a packet header, flow statistics (Counters), and Instructions defining the content of processing applied to a packet matching a matching rule (Header Field) is defined for each flow (refer to the section of “4.1 Flow Table” in Non-Patent Literature 2).
For instance, upon receiving a packet, the OpenFlow switch searches for an entry having a matching rule that matches the header information of the received packet in the flow table. When an entry matching the received packet is found as a result of the search, the OpenFlow switch updates the flow statistics (Counter) and performs the processing content (packet transmission from a designated port, flooding, discard, etc.) written in the action field of the entry on the received packet. Meanwhile, when no entry matching the received packet is found as a result of the search, the OpenFlow switch forwards the received packet to the OpenFlow controller via the secure channel, requests the OpenFlow controller to determine the path of the packet based on the source and the destination of the received packet, and updates the flow table after receiving a flow entry realizing this operation. As described, the OpenFlow switch forwards packets using entries stored in the flow table as processing rules.
Patent Literature 2 proposes a method that sets path information for all network (NW) devices utilizing packets, to which a list of path information (entries in the flow table set by the OpenFlow switch) is added, without having controllers communicate with each other in an environment where a network (NW) device and an incompatible network (NW) device coexist. Patent Literature 1, in Paragraph 0029 and below, introduces a configuration in which the OpenFlow is applied to a large-scale network such as a data center, and a plurality of controllers share the responsibilities of managing all network (NW) devices (refer to FIG. 4 as well).
Patent Literature 1
    International Publication Number WO2008/095010Patent Literature 2    Japanese Patent Kokai Publication No. JP-P2011-166704A[Non-Patent Literature 1]    Nick McKeown, et. al. “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched on Feb. 14, 2012], the Internet <URL: http://www.openflow.org/documents/openflow-wp-latest.pdf[Non-Patent Literature 2]    “OpenFlow Switch Specification” Version 1.1.0 Implemented (Wire Protocol 0x02), [online], [searched on Feb. 14, 2012], the Internet <URL: http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf>[Non-Patent Literature 3]    “OpenFlow Switch Specification” Version 1.0.0 Implemented (Wire Protocol 0x01), [online], [searched on Feb. 14, 2012], the Internet <URL: http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf>